1. Field of the Invention
The present invention relates to a temperature control apparatus, a processing apparatus, and a temperature control method, and particularly to a temperature control apparatus including a resistance heater for heating devices and controlling a temperature of the resistance heater, a processing apparatus including the temperature control apparatus, and a method for controlling the temperature.
2. Description of Related Art
In recent years, a fuel cell has attracted attention as a clean power source having high energy conversion efficiency, and the practical application of the fuel cell to a fuel cell powered vehicle, an electric home, and the like, has been advanced. Moreover, the research and development for using a fuel cell as a power source also in portable electronic equipment, such as a cellular phone and a notebook-size personal computer, has advanced.
A fuel cell is a device for producing electric power by electrochemical reactions between hydrogen and oxygen. The hydrogen to be supplied to the fuel cell is produced from, for example, a liquid fuel, such as methanol. In this case, a reaction apparatus for producing the hydrogen from a liquid fuel and water is connected to the fuel cell.
The reaction apparatus is composed of, for example, a vaporizer to vaporize a liquid fuel and water, a reformer to cause the reforming reaction of the vaporized fuel and water to produce hydrogen, and a carbon monoxide remover to remove the carbon monoxide infinitesimally produced in the reformer by means of the oxidization thereof. As such a reaction apparatus, a reaction apparatus integrally forming the reformer and the carbon monoxide remover was also developed. Specifically, the reaction apparatus is composed of a joined body of a plurality of substrates, grooves are formed on the joint surfaces of these substrates, catalysts are carried on the wall surfaces of the grooves, and the substrates are joined with one another so that the grooves may be covered by the substrates to function as the flow paths of the reformer and the carbon monoxide remover.
Moreover, since the reformer and the carbon monoxide remover have temperatures at which the reaction occurs efficiently and the temperatures are higher than a room temperature, it is necessary to heat the reformer and the carbon monoxide remover, and to control the temperature of the reformer or of the carbon monoxide remover so as to maintain the optimum temperature thereof.
In order to keep the temperatures of the reformer and the carbon monoxide remover at the optimum temperatures, it is general to use a feedback control method. That is, the reformer and the carbon monoxide remover are heated by a resistance heater; the temperatures of the reformer and the carbon monoxide remover are measured with temperature sensors, such as thermocouples; the measured temperatures are fed back; and the electric power to be supplied to the resistance heater is controlled on the basis of the measured temperatures. The reformer and the carbon monoxide remover can be thereby kept at the optimum temperatures.
Moreover, if the resistance value of the resistance heater depends on the temperature, then the temperature can be measured on the basis of the resistance value of the resistance heater, thereby the temperature sensor can be omitted. In this case, the current flowing through the resistance heater is controlled while the voltage across the resistance heater is measured with an operational amplifier and the like. In other words, a magnitude of the current to be applied to the resistance heater is set; the current of the magnitude is flown through the resistance heater; and the voltage across the resistance heater is measured with the operational amplifier to be fed back. The resistance value of the resistance heater is then obtained from the set magnitude of the current and the measured voltage, thereby the temperature of the resistance heater is also obtained. The magnitude of the current is newly set on the basis of the obtained resistance value or the obtained temperature, and the current of the newly set magnitude is flown through the resistance heater.
However, since a certain power source voltage is generally applied to a circuit including a resistance heater, even when the current flowing through the resistance heater is adjusted, electric power is consumed in some part other than the resistance heater so that heat is produced in the circuit by the consumption of the useless electric power.
Moreover, if the current of the resistance heater is enlarged, then the response voltage across the resistance heater also becomes larger. It becomes necessary to widen the range of the input voltage across operational amplifier for measuring the response voltage across the resistance heater, or to divide the input voltage and to attenuate the divided voltages in respective voltage ranges with an attenuator or the like, accordingly. The resolution capability of the measurement of the response voltage across the resistance heater falls and the causes of errors of the measurement increase.